The present invention relates to a method of in-line monitoring for a shallow pit. More particularly, the present invention relates to a method of in-line monitoring for a shallow pit on a semiconductor substrate while manufacturing a semiconductor device.
The shallow trench isolation (STI) process is one response to increasing densities in semiconductor devices. However, an impurity or a vacancy formed on the semiconductor substrate during the shallow trench isolation process often becomes a shallow pit. For example, shallow pit formation may occur during subsequent annealing steps. The shallow pit may cause bit failure or refresh failure, thus, reducing the manufacturing yield for the semiconductor device. Once formed, shallow pits cannot be completely removed. Thus, process conditions or process steps likely to form shallow pits must be understood, monitored, and remedied where reasonably possible.
These requirements prove problematic since shallow pits cannot be detected without the aid of an additional chemical process. In other words, since the shallow pit exists on the semiconductor substrate it does not affect the surface morphology of the semiconductor device under manufacture. Accordingly, the generation of shallow pits cannot be automatically monitored by a conventional image measuring apparatus designed to detect surface morphology or pattern distortion. This being the present case, shallow pit monitoring is done by manually scanning the semiconductor substrate using a conventional magnifying apparatus. This conventional process is, however, unacceptable. Shallow pit monitoring by manual means cannot be trusted and reliability cannot be ensured.
The only other conventional remedy determines shallow pit generation through feedback data obtained by testing the completed semiconductor device. This method wastes a great deal of time. Further, it is difficult to correlate the feedback data with the processing conditions or steps causing shallow pit formation.